SESKStuff Everyone Should Know
SESK: Stuff Everyone Should Know · sesk.info/tech-secure-boot

With UEFI Secure Boot turned on, what does the firmware check before running boot software?

Its digital signature, so only trusted code can start.

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  1. Its digital signature ✔
  2. Its file size
  3. How recently it was updated

Why: Secure Boot checks each boot component's signature against firmware trust and revocation databases. Trusted software can run, while untrusted or revoked software is blocked. This helps stop malware from loading before the operating system.

Huh, didn't know that: Firmware stores an allowed-signature database, a revoked-signature database and keys used to authorize updates.

The dad joke
Why did Secure Boot stop the bootloader? It forgot to sign the guest book.
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References

Answer: Its digital signature. Secure Boot checks each boot component's signature against firmware trust and revocation databases. Trusted software can run, while untrusted or revoked software is blocked. This helps stop malware from loading before the operating system.

  1. Microsoft Learn: Secure Boot learn.microsoft.com/en-us/windows-hardware/design/device-experiences/oem-secure-boot
    When the PC starts, the firmware checks the signature of each piece of boot software
    Checked 2026-10-10.

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